This invention relates to a method of restoring a picture cell by estimation with high density in a copying machine.
FIG. 1 shows a picture consisting of nine equal square picture cells obtained by sampling a copying original.
Heretofore, in restoring the central picture cell X by estimation, the estimation is carried out by approximation over linear polynominals including the density data of the eight picture elements A, B, C, D, E, F, G and H surrounding the central picture cell X. The estimation coefficients of the picture cells B, D, E and G are about 0.5, and those of the picture cells A, C, F and H are about -0.25 for Japanese and European languages if they are of a sentence pattern. Therefore, in estimating the central picture element X, there is no substantially great difference in picture quality between the case where all of the picture cells A through H are utilized and the case where only four picture cells B, D, E and G are utilized. This is due to the mutual relations between the central picture cell X and the surrounding picture cells A through H. In other words, the estimation is greatly affected by the picture cells B, G, D and E which are positioned above, below, at the left-hand side and at the right-hand side of the central picture cell X, and is not so affected by the remaining picture cells A, C, F and H.